One of the key manifestations in HIV infection is thrombocytopenia which was described even prior to the discovery of HIV. This grantee is investigating the role of various gene products in regulation of megakaryocytopoiesis and the effect of HIV infection on megakaryocytic cells. One such gene product, termed megakaryocyte associated tyrosine kinase, will be studied with respect to its expression in HIV infection. Initial results indicated an inhibitory effect of HIV on expression of these genes. The results of these studies will provide one mechanism for retroviral impairment of megakaryocyte growth and maturation.